The present invention relates to a test device for radiography and angiography systems and, more particularly, to a test phantom and method of fabrication and use of the same which incorporates stable iodine and other specific test details into a human tissue equivalent material in terms of attenuation and scatter.
As is known, angiography is the diagnostic study of the human cardiovascular system by the injection of iodine contrast materials into either the veins or arteries of a patient and the acquisition of X-ray images of the same cardiovascular system. Digital radiography and digital subtraction angiography are recent developments providing digital electronic X-ray imaging utilizing an X-ray imaging intensifier and a video system in combination with a computer. In addition to other advantages, such technology permits digital subtraction of images whereas one image of the body is taken prior to iodine contrast media injection and a second image is taken following the injection; with the two images then being compared, i.e. by digital subtraction, in the computer to provide an enhanced image of the blood vessels filled with contrast media while removing the overlying influence of bone and other soft tissue. In addition, the sensitivity of digital subtraction angiography systems is in general higher than with conventional film angiography thereby allowing the imaging of lower iodine concentrations in the patient.
The detection of small iodine concentrations in the cardiovascular system thereby facilitates imaging of the blood vessels, in some cases by injection of contrast media into the venous system, a procedure which reduces the risk to the patient while providing cost and time savings to the radiologist. Thus, digital angiography systems have become commercially successful in recent years and are finding widespread use in medical clinical applications throughout the world.
To insure the sensitivity of such digital subtraction angiography systems, however, a test assessment of the performance and imaging capability of such systems is imperative. Although there have been various prior art methods derived for testing and determining system performance, a preferred measurement method comprises the measurement of the level of iodine detectability under the digital subtraction mode of operation of such systems. Properly implemented, this measurement correspond to the systems ability to detect blood vessels of various diameters filled with various concentrations of iodine contrast media. One prior art system for providing an iodine detectability test is that developed by Riederer et al. (Riederer S. J., Di Bianca FA, Georges JPJ et al. Perfound Characteristics of a Digital Fluorographic System, Application of Optical Instrumentation in Medicine IX, SPIE Vol. 273, pp. 88-95. 1981) who constructed a subtraction test phantom using a liquid plastic manufactured by Clear Cast American Handi-Craft Company which solidifies in the presence of a catalyst. The solidified plastic may then be machined to form various channels or holes of desired diameter. Iodo-benzene, an iodine containing substance, is then desolved within a fluid liquid plastic and poured back into the machined channels within the plastic form thereby resulting in a test phantom.
The major problem associated with such prior art test phantoms has been their inability to maintain iodine in a stable format within the phantom over prolonged periods, resulting in the iodine propagating out of the test phantom. Thus, due to this instability of the iodine within the phantom, the use of such prior art phantoms to access performance of digital angiography systems over the normal course of system operation has been deficient.
In addition to the iodine instability deficiencies, the prior art phantom devices have also typically failed to provide a medium which simulates the properties of human blood vessels containing iodine. A third material used for a container of the iodine has not typically been tissue equivalent. As will be recognized, the use of such tissue equivalent media is imperative to insure proper system function during actual angiographic performance applications.
Further, the prior art test phantoms have typically been deficient in providing other non-iodine bearing test details in geometrically fixed positions within the phantom to permit accurate and reproduceable measurement of other parameters of digital X-ray imaging system performance such as video time jitter, system motion, and other error sources in subtraction imaging.
Thus, there exist a substantial need in the art for an improved test phantom representative of human tissue containing small concentrations of iodine in a long-term stable format which additionally includes other test details in geometrically fixed positions to provide a convenient method to accurately determine performance of digital subtraction angiographic systems.